1. Field of the Invention
The subject invention relates to an exhaust muffler manufactured from formed components. The muffler provides several acoustical tuning options for efficiently attenuating the noise associated with the flow of exhaust gas.
2. Description of the Prior Art
The most commonly used prior art exhaust muffler includes a plurality of separate parallel tubes that are supported by transversely extending planar baffles of oval or circular shape. The assembly of tubes and baffles is slid into a tubular shell that has a cross-sectional configuration conforming to the shape of the baffles. An outer wrapper may be wrapped around the shell for additional strength and noise insulation. Opposed end caps or headers are then mechanically connected to the opposed ends of the shell and wrapper to enclose the muffler. Each end cap includes an aperture to define an inlet to or outlet from the muffler. With this construction, chambers are defined within the prior art muffler between adjacent baffles or between a baffle and an end cap. Each chamber is enclosed by the tubular outer shell. Some of the tubes in the prior art muffler may terminate in a chamber. Others will pass entirely through a chamber. Portions of tubes in certain chambers will have louvers or perforations to permit gas communication between the tube and the surrounding chamber.
Exhaust gas in the above described prior art muffler flows from tubes into the surrounding chambers and from the chambers into other tubes. The particular pattern of exhaust gas flow will vary from one muffler design to another. However, many prior art mufflers utilize a tri-flow pattern. Exhaust gas enters the upstream end of a tri-flow muffler and flows to a reversing chamber near the opposed downstream end. The exhaust gas then undergoes a substantially 180.degree. change in direction and flows back toward the upstream end of the muffler to a second reversing chamber. The exhaust gas then undergoes a second 180.degree. change in direction and continues from the second reversing chamber to the outlet at the downstream end of the muffler. Perforated portions of the tubes pass through expansion chambers in the prior art muffler to permit expansion and cross flow of exhaust gas and to achieve attenuation of a major portion of the noise. Some non-perforated tubes may dead end into an enclosed Helmholz chamber to attenuate any narrow range of low frequency noise that is not adequately attenuated by the expansion chamber. The acoustical performance of this prior art muffler can be changed considerably by varying the dimensions of the tubes and chambers and by changing the size and locations of apertures, louvers or the like.
The above described prior art muffler is effective in attenuating noise. However, these prior art mufflers require a large number of separate components that must be assembled in a labor intensive manufacturing process. Furthermore, the abrupt edges of the tubes and the right angle alignment of the outer shell to the baffles, contribute to turbulence and back pressure that can impede engine performance.
The prior art also includes mufflers made entirely or substantially from formed sheets of metal. Very effective prior art formed mufflers are shown in patents assigned to the assignee of the subject invention. Most of these prior art formed mufflers include a pair of plates that are stamp formed with channels. The plates are secured in opposed face-to-face relationship, such that the channels define gas passages or tubes between the plates. These prior art stamp formed mufflers further include at least one external shell secured to at least one of the plates to define at least one chamber surrounding the gas passages or tubes formed by the plates. The tubes may be perforated to provide gas communication with the chambers defined by the external shell. These prior art stamp formed mufflers are shown in U.S. Pat. No. RE 33,370 and Reexamined U.S. Pat. No. 4,736,817.
Further improvements to stamp formed mufflers are shown in U.S. Pat. No. 5,252,788 which also is assigned to the assignee of the subject invention. The plates of the muffler shown in U.S. Pat. No. 5,252,788 are formed to define tubes and to further define an in-line chamber. The in-line chamber is bridged by a conventional tube disposed at a central location between the respective sides of the muffler. Exhaust gas entering this prior art muffler will flow through a formed inlet tube and will expand into the in-line chamber formed between the plates. The exhaust gas will then flow around opposite respective sides of the conventional tube and will expand a second time into portions of the in-line chamber downstream from the conventional tube. The exhaust gas will then enter a formed flow tube that communicates with the in-line chamber. The flow tube may be perforated or louvered to permit expansion of exhaust gas into a chamber defined by the external shell. The exhaust gas will continue into a second flow tube which communicates with the conventional tube that bridges the in-line chamber. Exhaust gas will continue through the conventional tube and toward the outlet of this prior art muffler. The in-line chamber formed by the plates extends into contact with the external shell of the muffler shown in U.S. Pat. No. 5,252,788. Thus, the in-line chamber can effectively function as a baffle between spaced apart chambers defined by the external shell.
The muffler shown in U.S. Pat. No. 5,252,788 has proved to be very effective and has been widely commercialized. However, it is desirable to provide even more tuning options in a muffler.
It is also be desirable to provide a muffler made entirely from formed components and having enhanced acoustical tuning capabilities.